Method of desulfurizing naphthenic acid



United States Patent METHOD OF DESULFURIZING NAPHTHENIC ACID Howard Packer and Glen Chalfant, Chicago, [1]., as-

signors to Witco Chemical Company, a corporation of Illinois No Drawing. Application March 16, 1953,

Serial No. 342,756

7 Claims. (Cl. 260-514) This invention relates to a new method of refining and purifying naphthenic acid and more particularly to a method for removing substantially all of the sulfur compounds from naphthenic acids.

Naphthenic acid recovered from certain crude petroleum contains appreciable amounts of sulfur compounds which are in the form of mercaptans, organic sulfides, cyclic sulfur compounds, and the like. The presence of even small quantities of these sulfur compounds in naphthenic acid is detrimental for certain end uses of the acid, particularly in the production of metallic soaps to be used in paint driers, gelling agents, mixing or suspending agents, and fungicides. In the preparation of metallic soaps from naphthenic acids, the metallic compounds used react with the sulfur compounds present in naphthenic acid producing finely divided, insoluble, and undesirable substances, such as metallic sulfides, which are diilicult and costly to remove. These insoluble compounds cause undesirable cloudiness and sludge formations in the compositions produced by incorporating the metallic soaps in liquid vehicles.

The presence of sulfur compounds also is undesirable in crude or semi-refined naphthenic acids which are to be refined fully for use in the preparation of ester-type plasticizers or light colored soaps. These sulfur compounds are not removed by the usual distillation process employed in the purification of naphthenic acids for these end uses. The sulfur compounds remain in the distillate and cause undesirable darkening because of oxidative changes.

In addition, the presence of sulfur compounds in naphthenic acid promotes corrosion of the equipment used for distillation.

Prior methods of desulfurizing employed in the petroleum industry, which involve treatments with doctor solutions or alkaline hypochlorites, not only are ineffective in removing sulfur compounds from naphthenic acid, but are not suitable for commercial production. The naphthenic acid would react with and dissolve in the alkaline solutions, and would thus require additional costly recovery processes.

The new method of this invention for removing sulfur compounds from naphthenic acid is markedly simple and efficient; requires a minimum of equipment; is well suited for use in purifying large amounts of naphthenic acid; and results in a large savings in cost and material.

Our new method consists essentially of heating naphthenic acid in the presence of hydrogen peroxide to at least a temperature sufficient to cause conversion of the sulfur compounds to volatile, oxidized, sulfur compositions. It has been found that conversion of the sulfur compounds is initiated at temperatures of about 200 F., but that a minimum temperature of about 260 F. must be attained to effect complete removal of all of the sulfur compounds withina reasonable time. The resulting converted sulfur compounds are removed from the naphthenic acid by volatilization. It is preferred to blow air through the naphthenic acid while it is being heated in the presence of hydrogen peroxide. By so doing, the naphthenic acid-hydrogen peroxide mixture is thoroughly agitated and at the same time the air materially aids in removing substantially all of the converted sulfur compounds and water from the naphthenic acid.

The amount of hydrogen peroxide to be used will vary, depending upon the amount of sulfur compounds present in the naphthenic acid to be treated. We have found that most naphthenic acids are effectively desulfurized 2,707,195 Patented Apr. 26, 1955 by employing an aqueous solution of hydrogen peroxide of about 15-35% strength in an amount. varying between about 0.5 to 5% of the weight of the naphthenic acid being treated. It is preferred to use an aqueous solution of hydrogen peroxide of about 30% strength, in an amount of about 13% by weight of the naphthenic acid.

Excellent results have been obtained by heating the naphthenic acid in a container to a temperature of from F. to 180 F., agitating the acid by blowing air from the bottom of the container through the acid, slowly adding the hydrogen peroxide solution to the agitated, heated naphthenic acid, and after adding the hydrogen peroxide solution, slowly raising the temperature of the resulting acid solution to at least 260 F. and preferably up to about 280 F., while continuing to blow air through the acid in order to complete the removal of volatile oxidized sulfur compounds and drive off any water from the naphthenic acid. The final temperature of the acid may be as high as 300 F. In order to avoid excessive foaming, it is preferred to start the addition of hydrogen peroxide when the naphthenic acid is at a temperature of about 180 F.

The naphthenic acids treated in accordance with the method of this invention may be used directly for the preparation of dark colored soaps, or may be distilled to obtain products of light color for use in making light colored soaps or esters.

A typical example illustrating the new method of this invention is as follows: 25,000 pounds of dark naphthenic acid (acid number equal to 205) derived from California crude oil was placed in an iron reaction vessel. This acid contained active sulfur as evidenced by the fact that when a polished strip of copper metal was kept immersed in it for three hours at C., the copper became coated with a black deposit of cupric sulfide.

The acid was heated to a temperature of about F. while agitating mechanically. 250 pounds of a 30% aqueous hydrogen peroxide solution were added slowly to the acid, then air introduced at the bottom of the vessel at a rate sufiicient to give good agitation to the mixture. Heating and blowing with air was continued for a period of about four hours, during which time the temperature was raised to about 280 F. Heating and air blowing was then discontinued and the desulfurized acid cooled to room temperature.

A bright strip of copper metal was kept immersed in the resulting naphthenic acid for three hours at 105 C., at which time the copper was found to be bright and free of black deposit. This was a clear indication that the corrosive sulfur present in the naphthenic acid prior to refining had been removed. To confirm this, a portion of the treated acid was fused with metallic sodium and the resulting solution tested with lead acetate. This test was negative, again indicating that no sulfur compounds of any type were left in the treated acid.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

We claim:

1. A method of removing sulfur compounds from naphthenic acid which comprises: heating naphthenic acid in the presence of hydrogen peroxide to at least a temperature sufficient to convert the sulfur compounds to volatile oxidized sulfur compositions and until substantially all of the sulfur compounds have been converted, and then volatilizing substantially all of the converted sulfur compounds from the naphthenic acid.

2. The method as set forth in claim 1, wherein the naphthenic acid is slowly heated in the presence of hydrogen peroxide to a temperature of at least: about 260 F. and not substantially greater than about 300 F. under normal atmospheric conditions to convert the sulfur compounds to volatile oxidized sulfur compositions and to volatilize substantially all of the sulfur compounds.

3. The method of claim 1, wherein from about a 15% to 35% aqueous solution of hydrogen peroxide is employed in an amount of from about 0.5% to 5% by weight of the naphthenic acid being used.

4. A method of removing sulfur compounds from naphthenic acid which comprises: heating naphthenic acid in the presence of hydrogen peroxide to at least a temperature sufiicient to convert the sulfur compounds to volatile oxidized sulfur compositions and until substantially all of the sulfur compounds have been converted, and volatilizing said volatile oxidized sulfur compositions while simultaneously blowing air through the naphthenic acid to agitate said acid and remove substantially all of the converted sulfur compounds therefrom.

5. The method of claim 4, wherein from about a 15% to 35% aqueous solution of hydrogen peroxide is employed in an amount of from about 0.5% to 5% by weight of the naphthenic acid.

6. The method of claim 4, wherein the naphthenic acid is slowly heated in the presence of hydrogen peroxide to a temperature of at least about 260 F. and not substantially greater than about 300 F. under normal atmospheric conditions to convert the sulfur compounds.

7. A method of removing sulfur compounds from naphthenic acid which comprises heating naphthenic acid to a temperature of from about 100" F. to 180 F., adding about a 15% to 35 aqueous solution of hydrogen peroxide in an amount from about 0.5% to 5% by weight of the naphthenic acid, raising the temperature of the resulting acid solution to at least about 260 F. and not substantially more than about 300 F. whereby to convert the sulfur compounds to volatile oxidized sulfur compositions and to volatilize said oxidized sulfur compositions, and blowing air through the naphthenic acid during both the initial and second heating periods to agitate said acid and remove substantially all of the converted sulfur compounds therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 1,886,647 Coleman Nov. 8, 1932 2,000,244 Merrill et al. May 7, 1935 FOREIGN PATENTS 408.663 Germanv Jan. 22 1925 

1. A METHOD OF REMOVING SULFUR COMPOUNDS FROM NAPHTHENIC ACID COMPRISES: HEATING NAPHTHECIC ACID IN THE PRESENCE OF HYDROGEN PEROXIDE TO AT LEAST A TEMPERATURE SUFFICIENT TO CONVERT THE SULFUR COMPOUNDS TO VOLATILE OXIDIZED SULFUR COMPOSITION AND UNTIL SUBSTANTIALLY ALL OF THE SULFUR COMPOUNDS HAVE BEEN CONVERTED, AND THEN VOLATILIZING SUBSTANTIALLY ALL OF THE CONVERTED SULFUR COMPOUNDS FROM THE NAPHTHENIC ACID. 